The ring-opening polymerisations of cyclic monomers like lactones or cyclic carbonates can normally be divided into two large categories anionic polymerisations using organometallic compounds as initiator and polymerisations using compounds having an active hydrogen such as water and alcohol as initiator and many sorts of broadly-called Lewis acids as catalysts.
The organometallic compounds used as initiators in the former anionic polymerisations may be illustrated by n-butyllithium, potassium tert-butoxide, sodium methoxide and a complex of rare earth metals. Specifically, JP-A46037737 describes the synthesis of a polystyrene-polycaprolactone block-copolymer or the like, JP-A-02029432 describes the synthesis of a polycaprolactone-polyneopentyl glycol carbonate block-copolymer and JP-A-05500982 and JP-A-05247184 describe the synthesis of a polycaprolactone by using a rare earth metal complex.
The advantage of such anionic polymerisations is that it is possible to synthesize a polymer or a block copolymer having a narrow molecular weight distribution. This is possible through the use of a special reaction method in which the solvent and the cyclic monomer used are highly purified
The catalysts of the latter polymerisations may be illustrated by sulphuric acid, para-toluenesulphonic acid, quaternary ammonium salts, boron trifluoride, tin tetrachloride, trialkyl aluminium, titanium (IV) butoxide, dibutyl tin oxide or other broadly-called Lewis acids.
These several sorts of Lewis acid act to lower the energy required to open the ring of monomers like lactone monomer and cyclic carbonate monomers. At the same time, they increase the nucleophilicity of initiators such as water or alcohols.
The initiator in ring-opening reactions is water or an alcohol. However, water and alcohol are at the same time reaction terminators and chain-transfer agents. Therefore, it is difficult to obtain a polymer or a block-copolymer having a narrow molecular-weight distribution according to such anionic polymerisation
Among polymerisations using broadly-called Lewis acids as catalysts, as a method which enables obtaining polymers and block-copolymers having a narrow molecular weight distribution, the method for synthesising a monodispersed lactone polymer is reported in Macromolecules 1987, 20, 2982-2988 by Inoue, Aida et al. This report describes the synthesis of a polycaprolactone polymer having a number-average molecular-weight of 1,100 to 10,400 measured by a GPC method and a molecular weight distribution value ranging from 1.10 to 1.18 by using an aluminium porphyrin complex as catalyst.
Further, in Makromol. Chem., Macromol. Symp. 1991, 42143, 117-133, Okamoto has synthesized a polylactone-diol polymer having a number average molecular-weight of approximately 3,000, measured by a GPC method, a molecular weight distribution value of approximately 1.25-1.31 by using triethyloxonium hexafluorophosphonate as a catalyst and ethylene glycol as initiator.
Moreover, according to EP 0600417 A1, it is possible to obtain a polymer having a molecular weight distribution value of approximately 1.7 to 2.1 via a ring-opening reaction of a cyclic carbonate and by using a hydroxyalkyl (meth)acrylate and polyvalent alcohols as initiators and an onium salt of an anionic Bronsted acid, strong acid ion-exchange resins, alkyl alkali metals, alkali metals alkoxides, amines, tin compounds, tungsten compounds, titanium compounds, or zinc compounds as catalyst.
On the other hand, recently, the use of necessarily high functional products and high added-value products has increased in fields like modifiers for resins, paints, modifiers for surface, adhesives or the like. Consequently, the needs for lactone polymers, carbonate polymers and lactone-carbonate copolymers having a narrow molecular weight distribution and a high purity regarding their single-structure components have also increased.
However, in order to obtain polymers of lactones having a specific structure or carbonate polymers via an anionic polymerisation method, a large amount of organometallic compounds have to be added as catalyst. Consequently, it is due to this large amount of organometallic compounds that several problems occur: it is difficult to control the reaction heat and the metallic components that remain seriously deteriorate the heat stability of the polymer.
Specifically, a one-step synthesis of methacrylic-modified lactone-polymer obtained by adding therein 2-hydroxyethylmethacrylate, 1 to 5 times mole amount of caprolactone is very difficult and not economically interesting via an anionic polymerisation.
Further, in the above-mentioned aluminium porphyrin system, the reaction speed is very slow and thus it takes more than ten days to synthesise the above-mentioned polycaprolactone polymers and the synthesised products are extremely coloured and thus cannot be used in practice.
Moreover, in the above-mentioned triethyloxonium hexafluorophosphonate system, a period of 24 hours at 30.degree. C. is necessary to obtain the polylactone-diol polymer and, moreover, about 5% of the lactone monomer remains ; on the other hand, the molecular weight distribution value increases when trying to improve the lactone monomer conversion to approximately 100%.
In order to solve such problems, the applicant has already discovered a method which is reported in JP-A-72920B3. This method consists in using specific aluminium-type Lewis acids as catalysts. According to this, it is possible to produce certain kinds of low dispersion polymers having a molecular weight distribution value of 1.0 to 1.5.
Lactone polymers and cyclic carbonate polymers are usually produced according to non-continuous processes. Particularly, in order to obtain high molecular-weight polymers, there are some difficulties in extruding such polymers due to their high viscosity which involve the unnecessary prolongation of heating time then deteriorating the physical properties of resins.
From the point of view of productivity increase, it is necessary to increase the reaction rate when increasing the amount of catalyst to be added. However, the non-continuous devices have generally limited heat transfer capacity.
In order to solve such a problem, a continuous process for producing lactones and cyclic carbonates has already been disclosed (EP-A-0 372 221 applied by Boehringer Ingelheim KG). In this document, the possibility of producing, in general, a poly-.epsilon.-caprolactone has been disclosed. However, a single catalyst and a single initiator have been disclosed. Moreover, in this document, for example, a tin salt such as stannous chloride and stannous octoate are mentioned as preferable. Further this method cannot be considered as suitable to continuously produce poly-.epsilon.-caprolactones in an extruder because of the recommended catalyst used to obtain industrially-allowable rate of conversion to poly-.epsilon.-caprolactones, and requires several hours for polymerisation.
According to a method using an extruder, the catalysts which may be used generally in an esterification reaction or a transesterification reaction are, for example, acetic salts of lead, zinc, manganese, calcium, cobalt, magnesium, antimony, aluminium, titanium, and tin etc., carbonates, halogenated compounds, oxides, alkylated compounds, alkoxides, particularly, halogenated compounds of aluminium, titanium, and tin, alkylated compounds, alkoxides or the like may be used. However, the molecular-weight distribution may be generally broad compared to a batch-type reactor.
JP-A07053686 proposes, from a point of view of improving the production rate, the use of aluminium alkoxides as polymerisation initiator to produce a poly-.epsilon.-caprolactone via an extruder. However, methods using metal alkoxides as polymerisation initiators are used to produce extremely high-molecular weight polymers as explained in JP-A-07053686. Thus, in the case of the production of relatively low molecular-weight polymers, there is a bad influence on physical properties and on the stability of the synthesised products due to the amount of metal contained in the resin.
Further, generally, in the case of a polymerisation reaction carried out in extruders or other continuous reaction device, the molecular weight distribution tends to be large because of the different portions of the reaction process which are not mixed each other. According to JP-A-07053686, it is possible to obtain polymers having a molecular weight distribution value of at least 2.2.
The purpose of the present invention is to provide lactone polymers, carbonate polymers, lactone-carbonate random copolymers and lactone carbonate block copolymers having a narrow molecular weight distribution or being monodispersed.
Another purpose of the present invention is to provide a continuous method for producing in a short time and efficiently the above-mentioned polymers.